Re: [PATCH 17/17] hwmon: (gl520sm) Fix overflows seen when writing into limit attributes

[Guenter Roeck <linux@roeck-us.net>]

On 12/13/2016 01:56 AM, Jean Delvare wrote:
> On Sun,  4 Dec 2016 20:55:40 -0800, Guenter Roeck wrote:
>> Writes into limit attributes can overflow due to multplications
>> and additions with unbound input values.
>>
>> Signed-off-by: Guenter Roeck <linux@roeck-us.net>
>> ---
>>  drivers/hwmon/gl520sm.c | 9 +++++----
>>  1 file changed, 5 insertions(+), 4 deletions(-)
>>
>> diff --git a/drivers/hwmon/gl520sm.c b/drivers/hwmon/gl520sm.c
>> index dee93ec87d02..4bb37d7234b1 100644
>> --- a/drivers/hwmon/gl520sm.c
>> +++ b/drivers/hwmon/gl520sm.c
>> @@ -209,10 +209,11 @@ static ssize_t get_cpu_vid(struct device *dev, struct device_attribute *attr,
>>  static DEVICE_ATTR(cpu0_vid, S_IRUGO, get_cpu_vid, NULL);
>>
>>  #define VDD_FROM_REG(val) (((val) * 95 + 2) / 4)
>> -#define VDD_TO_REG(val) clamp_val((((val) * 4 + 47) / 95), 0, 255)
>> +#define VDD_TO_REG(val) \
>> +	DIV_ROUND_CLOSEST(clamp_val(val, 0, 255 * 95 / 4) * 4, 95)
>>
>>  #define IN_FROM_REG(val) ((val) * 19)
>> -#define IN_TO_REG(val) clamp_val((((val) + 9) / 19), 0, 255)
>> +#define IN_TO_REG(val) DIV_ROUND_CLOSEST(clamp_val(val, 0, 255 * 19), 19)
>>
>>  static ssize_t get_in_input(struct device *dev, struct device_attribute *attr,
>>  			    char *buf)
>> @@ -514,8 +515,8 @@ static DEVICE_ATTR(fan1_off, S_IRUGO | S_IWUSR,
>>  		get_fan_off, set_fan_off);
>>
>>  #define TEMP_FROM_REG(val) (((val) - 130) * 1000)
>> -#define TEMP_TO_REG(val) clamp_val(((((val) < 0 ? \
>> -			(val) - 500 : (val) + 500) / 1000) + 130), 0, 255)
>> +#define TEMP_TO_REG(val) (DIV_ROUND_CLOSEST(clamp_val(val, -130000, 125000), \
>> +					    1000) + 130)
>>
>>  static ssize_t get_temp_input(struct device *dev, struct device_attribute *attr,
>>  			      char *buf)
>
> Reviewed-by: Jean Delvare <jdelvare@suse.de>
>
> But I think FAN_TO_REG can overflow too? Input value is left-shifted
> without a prior check.
>
You are right. My older script didn't detect that because the overflow happens
with a very low value, and the script just concluded that the value range was [0,0].

After improving my test script, the driver generates KASAN bad memory reports.
Outch. I'll have to look into that.

Thanks,
Guenter